As shown in Fig. 6, bioaerosol microbial activity on hazy days was higher than on sunny days in the spring, autumn and winter. The average value on hazy days was 1.28 times that on sunny days; this trend was especially true in the autumn and winter. This result is consistent with previous studies that determined that under different haze levels the concentration of total bacteria and fungi were negatively correlated with AQI (PM2.5), an indicator of hazy days (Gao et al., 2015). Studies have shown that the concentration of bacteria and yeasts in the air is greatly influenced by the chemical composition and acidity of fog droplets (Fuzzi et al., 1997). The fog droplets may act as culture media for microbes to attach to and may also provide nutrients for their growth and reproduction, thus enhancing the microbial activity. However, this situation was not the same case for the samples in the spring, when the microbial activity was lower on hazy days (March 5, April 25, and May 25) than on sunny days. These differences may be partly due to the changes in environmental conditions in different seasons.